In the SCA-period Ottoman Empire, gömleks are, in essence, undershirts. They were therefore worn, by both genders, as the bottommost layer of garment for their upper bodies. It's a well-known garment that is referenced in many period works, and worn by almost everyone in the region during late SCA period. The act of researching the gömlek, however, is also a prime example of a major issue with re-creating a complete Ottoman outfit. Underclothes are rarely displayed in images without the accompanying over clothes , an issue which hides details of fit and construction. In addition, written descriptions fail to give the kind of details that help re-creational efforts. As well, the Ottoman clothing was such that outer layers were sumptuous, coveted items, kept through many generations, but the inner layers, worn next to the skin, were more-or-less disposable. Gömlek - either goomlek (oo as in moon) or gumlek (u as in gum), i'm not sure which. This is the basic undergarment, a sheer white tunic that pulls on over the head, with a long slit in the center front. I know of none that have survived from the SCA-period Ottoman Empire. In art, there is no complete picture of a woman's gömlek, for reasons of modesty. The hem falls to mid-calf, or sometimes to the ankle. The "skirt" is quite full. Usually the sleeves are voluminous and quite wide at the wrist, draping without drawstrings or ties. The fabric is quite sheer and there appears to be embroidery on or along the seams.
Since we are not certain what they were made of "in period", I use white cotton batiste, which is a very light sheer cotton. One could also use handkerchief linen as sheer as you can fine, or lightweight china silk/ silk habotai. I recommend cotton or linen for their washability and functionality, particularly in dealing with bodily moisture. If you plan to wear this in hot humid weather, i recommend linen, which is cooler than cotton. White wool might have been used in winter. It is very cold in a stone house with no central heating in Eastern Europe or Anatolia in winter, and some men's wool gömleks survive from later times.
This information taken from Dar Anahita, the website of Urtatim al-Qurtubiyya. Thanks Urtatim!